1. Field of the Invention
This invention relates to a method of manufacturing methanol.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Publication No. 1-180841 discloses a method of manufacturing methanol (CH3—OH) from hydrocarbon such as natural gas. Specifically, this publication describes a method of manufacturing methanol, which comprises:                reacting a gaseous hydrocarbon or a vaporized liquid hydrocarbon, by making use of a reformer, with water vapor in the presence of a nickel catalyst at a temperature ranging from 800 to 1000° C. to produce a synthesis gas comprising, as main components, hydrogen (H2), carbon monoxide (CO) and carbon dioxide (CO2);        allowing reaction of the synthesis gas to take place over a copper-based methanol-synthesizing catalyst which is placed inside a synthesis reactor at a pressure of 50 to 150 atm and at a temperature of 200 to 300° C. to produce a reaction product;        cooling the crude methanol;        separating the cooled crude methanol into unreacted gas and liquid crude methanol; and        distilling the liquid crude methanol in one or more distillation columns to separate refined methanol and a waste water containing organic compounds having a lower boiling point than that of methanol (hereinafter, referred to as low boiling point organic compounds), another organic compounds having a higher boiling point than that of organic acid and methanol (hereinafter, referred to as high boiling point organic compounds).        
In the aforementioned synthesis gas-producing step, by making use of a carbon dioxide recovery apparatus, carbon dioxide is recovered from a combustion exhaust gas which has been discharged from the reformer, and the carbon dioxide thus recovered is fed to the upstream side of the reformer and/or the downstream side of the reformer to obtain a synthesis gas having a desired molar ratio of H2/(CO+CO2) which is suitable for the manufacture of methanol.
However, as the quantity of carbon dioxide to be recovered by the carbon dioxide recovery apparatus is increased in the conventional method of manufacturing methanol, the heat quantity required to be used in the carbon dioxide recovery apparatus is caused to increase correspondingly, thus inviting a shortage of heating sources and hence increasing the manufacturing cost of methanol.